Electric ship propulsion



Fdwo 5 E929; 113M582 c. MACMILLAN;

ELECTRIC SHIP PROPULSION Filed March 21, 1924 2 Sheets-Shem l Inventor: Campbei! macrnilian,

y M Q His Attorney.

Fsh 5 192% C MACMI LLAN ELECTRIC SHIP PROPULSION Filed March 21, 1924 2 sheets She-ec Fig.3..

Inventor Campbell macmiiian,

f Y by 2% His Attorney.

CAMPBELL HACMELAN, OF SGHENECTADY, NEW YORK, ASSIGNOR PAT ENT OFFICE- TO GENERAL ELEC- TRIO COMPANY, 'A CORPORATION OF NEW YORK.

ELEUIRIC SHIP PROPULSION.

Application flled larch 21, 1924. Serial 170; 700,972.

My invention relates to electric ship propulsion, and has for its object the provision of an improved propulsion system which is capable both of being controlled in a simple manner and of being efiiciently operated at the difi'erent driving speeds of the ship.

The power consumed in driving a ship varies approximately as the cube of the ships driving speed. For this reason the torque required to be exerted by the propeller motors varies over a wide ran e. Thus, if the ship is to be driven at spee s in the ratio of 1 to 2, for example, the propeller motors will be required to supply at the higher speed an amount of power about eight times that required at the lower speed.

Where there are two or more motors per propeller shaft it is of course possible to disconnect a part of the motors on each shaft during low speed operation and to operate the remaining motors at a fairly high efiiciency. It is not possible to do this in cases where a single motor per shaft is used and, if induction motors are used, the motor efliciency at the lower speeds is unsatisfactory.

The induction motor is required to establish its own field and for this reason always operates at a power factor which is somewhat below unity. Due to the fact that the value of its magnetizing current is dependent upon the voltage applied to its primary coils rather than upon the motor load, the ower factor of this motor is especially be when it is operated at light loads. In the application of induction motors to ship propulsion it is therefore desirable to provide means for reducing the voltage per coil when the motor is operated to. drive the ship at its cruising speed. In accordance with my invention this is accomplished by changing the connections of the motor primary coils from two circuit delta to single circuit Y. Y I

My invention will ,be better understood from the following description when considered in connection with the accompanying drawing, and its scope will be pointed out in the appended claims.

Referring to the drawing, Fi 1' shows a system of ship propulsion in w ich my 1nvention has been embodied: and Figs. 2, 3 and 4 show certain details in the connections of the motor primary coils.

Fig. 1 shows four similar units each comprising afiopeller motor-1 havingits primary win g 2 arranged to be supplied with of the motors 1 is Suitable switches 12 are provided for interconnecting the various units.

Fig. 2 shows how the controllers 6 are utilized to alter the connections of the coils 13, 14, 16, 17, 19 and 20 of a primary winding 2. It will be observed that the outer ends of the coils 13', 16 and 19 are permanentl connected to the lines 15, 18 and 21 througi which current is supplied to the motors from the generators 3. The two operating positions of the controller 6 are indicated by the legends Low speed and High speed. When the controller is moved to its Low speed position the inner ends of the coils 14, 17 and 20 are interconnected to form a single circuit star or Y-connection as indicated in Fig. 3. .-With this connection the voltage per coil is comparatively low due both to the series arrangement of the coils and to the fact that they are connected in star. Asa result of this reduction in the voltage per coil the magnetizing current of the motor is decreased and the power factor at which the motor operates is correspondingly improved.

To increase the motor speed the controller 6 is moved to its High speed position. This opens the Low speed connection at the Y point and connects these same points to the line. The midpoints of the series connected coils of each phase are also connected at this time to the line. In this position the various coils are interconnected in a double delta circuit as shown inFig. .4 and the full line" voltage is applied to each coil. The reversal of current in half of the coils in each phase results in halving the number of poles and this gives the higher speed of operation. The motors are thus arranged to exert their maximum torque.

When it is desired to reverse the direction of propeller rotation the speed and excita tion of the generators 3 \is reduced, the switches 4 are operated to reverse the phase rotation between the generators and motors, the controller 6 is moved to its Low speed position and exciting current is supplied to the generator field windings 9.

With the Low speed connection, the eftective impedance of the motors is increased. This makes it possible for the generators to deliver more nearly their maximum kilovolt amperes and with the proper increase in the voltage of the generators, insures adequate torque for the purpose of reversal. This makes it possible to utilize motors designed to operate at high power factor while running although the motor torque and power factor at starting may be comparatively low and is, the means of effecting marked economies in the operation of the ship as will be readily understood by those skilled in the art.

What I claim as new and desire to secure by Letters Patent of the United States is l. The method of operating a three-phase electric ship propulsion system in which there is only one propeller driving motor per pro- .peller shaft, such motor having aplurality nected to pro uce two pole numbers in the ratio of l to 2, and means for connecting said coils in single circuit star of the higher pole number for low-speed operation andfor reversal and in double circuit delta of the lower pole number for high-speed operation.

3. The method of bringing up to speed a squirrel cage three-phase motor having a plurality of winding coils in each or its phases which includes first operating the motor with the coils connected in single circuit star to produce one number of poles, and then operating the motor with the coils connected in double circuit delta with half the coils rcversed to produce half such number of poles.

i. In combination, a three-phase induction motor having two groups of winding coils per phase, the free ends of three of said groups being respectively permanently connected to terminals constituting iine termi--' nals, the other ends of said three groups be ing permanently connected to the respective ends of the other three of said groups and provided with terminals constituting intermediate terminals, means for connecting the free ends of said other groups together to connect said two groups of windings in single circuit star for one pole number, means for connecting said last-mentioned free ends respectively to the correspondh'ig line terminals with the star point open, and means for connecting each line terminal respectively to the next intermediate terminal to connect said two groups of windings in double circuit delta for half such pole number.

In witness whereof, I have hereunto set my hand this 20th day of March, 1924.

CAMPBELL MACMILLAN.

CERTIFICATE or connection;

Patent No. 1,70i,3s2.

Granted r brusr s, i929, a

CAMPBELL MACMILLAN.

lt is, hereby certified that error appears in above numbered patent requiring correction as follows:

for the word' 'mcmbers" read "numbers";

be read with this correction therein that the. case in the Patent Office.

Signed and sealed this 5th, day of Ma rch, A. 1). 1929.

M. J. Moore, Acting Commissioner oi Patents.

CERTIFICATE OF CORREGTKON.

Patent No. 1,701,382. Granted February 5, 1929, to

CAMPBELL MACMILLAN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, line 26, claim 1, for the word "members" read "numbers"; and that the said Letters Patents should be read with this correction therein that the same may conform to the record of the ease in the Patent ()ffice 4 Signed and sealed this 5th day of March, A. Dr 1929.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

